APTech AP74B - Manual (Page 3)

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Manual 15000002 Rev 2 Page 3 of 4
2. Capacitive loads – when a capacitor is provided in series or in parallel with the reed
switch contacts in a closed circuit, the in rush current, which flows at the time of charge
and discharge of the capacitance, will cause deterioration of the reed contacts. The two
figures shown below are typical examples of the protection circuits used to prevent in
rush current.
Current limiting resistor (R
K
) is installed to protect
contact .
Resistor (R) is installed to protect contact. R should
be between 50 and 500 Ohm.
3. Lamp loads – when a lamp load is used with the reed switch, the in rush current can cause
deterioration of the reed contacts. The follow two figures show examples of protection
circuits.
Current limiting resistor (R) is installed to protect
contact. R should be determined to satisfy:
Is < 0.2A
Parallel resistor (R) is installed to preheat lamp
filament and increase the resistance. R should be:
R < Filament resistance / 3